1. Field of the Invention
The present invention relates to a material useful for introducing a coating film onto the top portion of a photoresist, and more particularly to, a top anti-reflective coating polymer which is introduced to the top portion of a photoresist which is introduced to top portion of a photoresist, its preparation method and a top anti-reflective coating composition comprising the same, in a process for forming ultra-fine patterns of photoresist for photolithography by using 193 nm ArF or 157 nm VUV light source.
2. Description of the Related Art
In a fabrication process of ultrafine patterns for preparing semiconductor devices, standing waves and reflective notching inevitably occur due to the optical properties of lower film layer on the photoresist film and due to thickness changes in the photosensitive film. In addition, there is another problem in that a CD (critical dimension) alteration is caused by diffracted and reflected light from the lower film layers. Thus, it has been suggested to introduce anti-reflective coating that prevents back reflection at a lower film layer between a lower film and a photoresist by introducing organic material with high absorbance at a wavelength range of the light employed as a light source.
Especially, when exposed to UV light from a light source, a photoresist thin film is transmitted by the UV light, thus allowing the light absorbed in the bottom portion of the thin film to be scattered and/or reflected. Such anti-reflective coating can absorb the scattered and/or reflected light and, thereby, directly affecting the fine processing of the photoresist.
However, as the patterns are becoming ultra-fine along with the reduction of semiconductor devices to less than 90 nm, it is difficult to completely prevent pattern alteration or distortion generated due to diffused reflection by only the above anti-reflective coating, that is, a bottom anti-reflective coating (hereinafter referred to as BARC) introduced between the bottom film layer and the photoresist. Therefore, it requires an improved anti-reflective coating material to be applied on top portion of the photoresist, which can greatly reduce and/or minimize the pattern distortion caused by the diffused reflection.
In processes for forming ultrafine patterns by using a light source with a wavelength of 157 nm, mostly used is a compound containing fluorine such as a photosensitive agent. Such fluorine based photosensitive compound has a problem that it is contaminated by amine compounds among the atmosphere, since carbon-fluorine bond in the photosensitive compound may form a strong hydrogen bond with a nitrogen-hydrogen bond in the amine compound.
In particular, during the patterning process, a time delay effect for a further process after exposure, a so-called post exposure delay effect, occurs and enlarges the contamination problem concerning the fluorine based photosensitive compound by atmospheric amine compounds such as ammonia. Therefore, a strong demand recently exists for an anti-reflective coating material or patterning process to minimize the contamination of photoresist film due to the post exposure delay.
Accordingly, due to such problems in the conventional art, there is a continuous demand for an additional anti-reflective coating material which can minimize contamination of the photoresist film caused by the amine compound even when it generates the post exposure delay after the exposure while having no adverse effect on the formation of patterns by exposure and development processes, in addition to, which can further reduce alteration or distortion of the pattern caused by the diffused reflection as the anti-reflective coating material is applied together with the conventional anti-reflective coating typically introduced on to the bottom portion of the photoresist, and a method for forming a pattern by employing such anti-reflective coating material.